Synthesis of biolubricant esters from unsaturated fatty acid derivatives

ABSTRACT

The present invention is generally directed to diester-based lubricant compositions comprising one or more isomeric mixtures of diester species. The present invention is also directed to methods of making these and other similar lubricant compositions. In some embodiments, the methods for making such diester-based lubricants utilize a biomass precursor material from which mono-unsaturated free lipid species can be provided or otherwise generated, wherein such mono-unsaturated free lipid species are converted to isomeric diol species en route to the synthesis of diester species for use as/in the diester-based lubricant compositions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending applicationSer. No. 12/498,663, filed Jul. 7, 2009 and claims priority therefrom.

FIELD OF THE INVENTION

This invention relates to ester-based lubricants and specifically todiester-based lubricants and their manufacture—particularly wherein theyare made from at least one biologically-derived precursor.

BACKGROUND

Esters have been used as lubricating oils for over 50 years. They areused in a variety of applications ranging from jet engines torefrigeration. In fact, esters were the first synthetic crankcase motoroils in automotive applications. However, esters gave way topolyalphaolefins (PAOs) due to the lower cost of PAOs and theirformulation similarities to mineral oils. In full synthetic motor oils,however, esters are almost always used in combination with PAOs tobalance the effect on seals, additives solubility, volatility reduction,and energy efficiency improvement by enhanced lubricity.

Ester-based lubricants, in general, have excellent lubricationproperties due to the polarity of the ester molecules of which they arecomprised. The polar ester groups of such molecules adhere topositively-charged metal surfaces creating protective films which slowdown the wear and tear of the metal surfaces. Such lubricants are lessvolatile than the traditional lubricants and tend to have much higherflash points and much lower vapor pressures. Ester-based lubricants areexcellent solvents and dispersants, and can readily solvate and dispersethe degradation by-products of oils. Therefore, they greatly reducesludge buildup. While ester-based lubricants are stable to thermal andoxidative processes, the ester functionalities give microbes a handle todo their biodegrading more efficiently and more effectively than theirmineral oil-based analogues. However, the preparation of esters is moreinvolved and more costly than the preparation of their PAO counterparts.

Diester-based lubricants and their manufacture have been recentlyreported, wherein the diester species have a general formula:

where R′₁, R′₂, R′₃, and R′₄ are the same or independently selected froma C₂ to C₁₇ carbon fragment. See commonly-assigned U.S. patentapplication Ser. Nos. 11/673,879 (Miller et al.), filed Feb. 12, 2007and published as United States Patent Publication No. US 20080194444 onAug. 14, 2008; and Ser. No. 12/023,695 (Miller et al.), filed Jan. 31,2008. Note that the two ester groups are vicinal in their attachment tothe aliphatic backbone of the diester species.

In view of the foregoing, and not withstanding such above-describedadvances in diester-based lubricant synthesis, facile methods ofgenerating diester-based lubricants would be extremelyuseful—particularly wherein the diester species in said lubricants candeviate from the vicinal arrangement of the esters groups in relation totheir aliphatic backbone.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is generally directed to diester-based lubricantcompositions, such compositions generally comprising one or moreisomeric mixtures of diester species. The present invention is alsodirected to methods of making these and other similar lubricantcompositions. In some embodiments, the methods for making suchdiester-based lubricants make at least partial use of one or morebiomass precursor species as reagents in the synthesis of such diesterspecies. Indeed, in some embodiments such diester-based lubricants canbe entirely bio-derived. In some or other embodiments, lubricantprecursor species can also be sourced or otherwise derived fromFischer-Tropsch (FT) reaction products/byproducts.

In some embodiments, the present invention is directed to at least onelubricant composition comprising a quantity of at least one isomericmixture of diester species, the diester species (1a) and (1b) having thefollowing structures:

wherein R₁, R₂, R₃, and R₄ are the same or independently selected fromC₂ to C₂₀ hydrocarbon groups, and wherein “n” and “m” are integers from2 to 20. In some such compositional embodiments, the isomeric diesterspecies, of which the at least one isomeric mixture is comprised, have amolecular mass that is from at least about 400 atomic mass units(a.m.u.) to at most about 1100 a.m.u., and more typically between 450a.m.u. and 1000 a.m.u.

In terms of physical and lubricative properties, in some embodiments thekinematic viscosity of the above-described composition at a temperatureof 100° C. is at least 3 mm²/s, i.e., 3 centistokes (cSt). In some orother embodiments, said composition has a pour point of less than −20°C. Typically, such properties are such that, in at least someembodiments, the compositions can be used as lubricants in one or moreof a variety of applications and environments.

In some embodiments, the above-described composition comprisesquantities of at least two different isomeric mixtures of diesterspecies—typically with large variability in relative amounts. In some orother embodiments, said composition further comprises a base oilselected from the group consisting of Group I oils, Group II oils, GroupIII oils, and combinations thereof. Additionally or alternatively, insome embodiments, said composition further comprises one or moremonoester and/or triester species.

In some embodiments, the present invention is directed to methods ofmaking the above-described composition(s), such methods comprising thesteps of: (A) converting a quantity of mono-unsaturated free lipidspecies (e.g., mono-unsaturated fatty acid(s) and/or ester(s)), having acarbon number of from 10 to 22, to an isomeric mixture of diol specieshaving the same carbon number as the free lipid species from which theywere derived, wherein said converting proceeds via an epoxideintermediate species; and (B) esterifying the isomeric mixture of diolspecies with an esterifying species to form an isomeric mixture ofdiester species, wherein the isomeric mixture of diester speciescomprises isomerically-related structures 1a and 1b, and wherein R₁, R₂,R₃, and R₄ are the same or independently selected from C₂ to C₂₀hydrocarbon groups, and wherein n and m are the same or independentlyselected from the group of integers 2 to 20.

In some such above-described method embodiments, the step of convertingcomprises the following sub-steps: (Substep A) epoxidizing the quantityof mono-unsaturated free lipid species to yield a quantity of epoxidizedlipid species; and (Substep B) reducing the epoxidized lipid species toyield an isomeric mixture of diol species—which is subsequentlyesterified to yield an isomeric mixture of diester species.

In some embodiments, variations on the above-described methodembodiments are found wherein the step of converting comprises thefollowing alternate (variational) substeps: (Alt. Substep A) reducingthe quantity of mono-unsaturated free lipid species to yield a quantityof mono-unsaturated fatty alcohol species; (Alt. Substep B) epoxidizingthe quantity of mono-unsaturated fatty alcohol species to yield aquantity of epoxidized alcohol species; and (Alt. Substep C) reducingthe epoxidized alcohol species to yield an isomeric mixture of diolspecies.

The foregoing has outlined rather broadly the features of the presentinvention in order that the detailed description of the invention thatfollows may be better understood. Additional features and advantages ofthe invention will be described hereinafter which form the subject ofthe claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts four exemplary isomeric diester pairs 2a-5a and 2b-5b,suitable for use as lubricants and/or lubricant components, inaccordance with some embodiments of the present invention;

FIG. 2 is a flow diagram describing how isomeric mixtures of diesterspecies are prepared, in accordance with some embodiments of the presentinvention;

FIG. 3 (Scheme 1) is a chemical flow diagram illustrating somerepresentative methods of making (synthesizing) a diester-basedlubricant composition (or at least a diester component thereof), inaccordance with some embodiments of the present invention, wherein oleicacid is used as a representative mono-unsaturated fatty acid;

FIG. 4 (Scheme 2) is a chemical flow diagram illustrating one or morealternate methods of making a diester-based lubricant composition (or atleast a diester component thereof), in accordance with some embodimentsof the present invention, wherein oleic acid is used as a representativemono-unsaturated fatty acid;

FIG. 5 (Scheme 3) is a chemical flow diagram illustrating methods ofmaking a diester-based lubricant composition (or at least a diestercomponent thereof) from oleic acid, in accordance with some embodimentsof the present invention, and as illustrated in Examples 1-4; and

FIG. 6 (Table 1) lists lubrication and physical properties of isomericdiester mixture 4a/4b, as prepared in Example 4.

DETAILED DESCRIPTION OF THE INVENTION

1. Introduction

The present invention is generally directed to diester-based lubricantcompositions comprising isomeric mixtures of diester species. Thepresent invention is also directed to methods (processes) of makingthese and other similar lubricant compositions. In many of theseembodiments, the methods for making such diester-based lubricantsutilize one or more biomass precursor species, wherein it is typicallyat least the lipid components utilized in such methods that are obtainedfrom biomass sources (e.g., vegetable oil and/or algae). Other chemicalcomponents used in such methods can be similarly derived from biomass,or they can be derived from other sources such as, but not limited to,Fischer-Tropsch (FT) synthesis products and/or by-products.

Because biolubricants and biofuels are increasingly gaining ground andbecoming topics of focus for many in the oil/petroleum industry, the useof biomass in the making of such above-mentioned lubricants could beattractive from several different perspectives. To the extent thatbiomass is so utilized in making the diester-based lubricants of thepresent invention, such lubricants are deemed to be biolubricants.

An advantage of the diester lubricants described herein, in at leastsome embodiments, is that they can be entirely bio-derived; i.e., all ofthe reagents used in their synthesis (generally exclusive of solventsand catalysts) can be derived from a biological precursor material.Additionally, methods for producing such lubricants make use of olefinsalready present in vegetable/crop oils, thereby streamlining thesynthetic process. Additionally still, as opposed to conventionalbiolubricants, i.e., triglycerides, the diester-based lubricantsdescribed herein have, in at least some embodiments, excellent lowtemperature properties without having carbon-carbon double bonds, thepresence of such bonds generally compromising the lubricantcomposition's oxidation stability.

2. Definitions

“Lubricants,” as defined herein, are substances (usually a fluid underoperating conditions) introduced between two moving surfaces so toreduce the friction and wear between them. Base oils used as motor oilsare generally classified by the American Petroleum Institute as beingmineral oils (Group I, II, and III) or synthetic oils (Group IV and V).See American Petroleum Institute (API) Publication Number 1509.

“Pour point,” as defined herein, represents the lowest temperature atwhich a fluid will pour or flow. See, e.g., ASTM Standard Test Method D5950-02 (R 2007).

“Cloud point,” as defined herein, represents the temperature at which afluid begins to phase separate due to crystal formation. See, e.g., ASTMStandard Test Method D 5771-05.

“Centistoke,” abbreviated “cSt,” is a unit for kinematic viscosity of afluid (e.g., a lubricant), wherein 1 centistoke equals 1 millimetersquared per second (1 cSt=1 mm²/s). See, e.g., ASTM Standard Guide andTest Method D 2270-04.

“Oxidation stability,” as defined herein, generally refers to acomposition's resistance to oxidation. Oxidator BN is a convenient wayto measure the oxidation stability of base oils, and it is the methodused to evaluate the oxidation stability of at least some of thelubricant compositions described herein. The Oxidator BN test isdescribed by Stangeland et al. in U.S. Pat. No. 3,852,207, which issuedon Dec. 3, 1974. The Oxidator BN test measures an oil's resistance tooxidation by means of a Dornte-type oxygen absorption apparatus. SeeDornte “Oxidation of White Oils,” Industrial and Engineering Chemistry,vol. 28, pp. 26-30, 1936. Normally, the conditions are one atmosphere ofpure oxygen at 340° F. (171° C.). The results are reported in hours toabsorb 1000 mL (1 L) of O₂ by 100 grams of oil.

With respect to describing molecules and/or molecular fragments herein,“R_(x),” where “x” is merely an identifier, refers to a hydrocarbongroup, wherein the molecules and/or molecular fragments can be linearand/or branched, and unless stated otherwise, groups identified bydifferent “x” identifiers can be the same or different.

As defined herein, “carbon number,” as it relates to a hydrocarbonmolecule or fragment (e.g., an alkyl group), is an integer denoting thetotal number of carbon atoms in the fragment or molecule. Carbon numberwith such a fragment or molecule can also be denoted as “C_(y)”, where“y” is the total number of carbon atoms within that particular fragmentor molecule.

“Triglyceride,” as defined herein, refers to class of molecules havingthe following molecular structure:

where x′, y′, and z′ can be the same or different, and wherein one ormore of the branches defined by x′, y′, and z′ can have unsaturatedregions.

A “carboxylic acid” or “fatty acid,” as defined herein, is a class oforganic acids having the general formula:

where “R_(n)” is generally a saturated (alkyl)hydrocarbon chain or amono- or polyunsaturated (alkenyl)hydrocarbon chain.

“Lipids,” as defined herein, broadly refers to the class of moleculescomprising fatty acids, and tri-, di-, and mono-glycerides.

“Hydrolysis” of triglycerides yields free fatty acids and glycerol, suchfatty acid species also commonly referred to as carboxylic acids (seeabove).

“Transesterification,” or simply “esterification,” refers to thereaction between a fatty acid or ester (e.g., a triglyceride) and analcohol to yield an ester species.

The term, “mono-unsaturated free lipid species,” as defined herein,refers to mono-unsaturated fatty acids and/or mono-unsaturated fattyesters—typically such species being derived from triglyceride speciesvia hydrolysis and/or transesterification, wherein at least some of thetriglyceride species comprise at least one mono-unsaturated fatty chain,i.e., a hydrocarbon chain having a single carbon-carbon double bond.

The prefix “bio,” as used herein, refers to an association with arenewable resource of biological origin, such as resource generallybeing exclusive of fossil fuels.

The term “bio-derived,” as defined herein, refers to derivation from arenewable biological resource, organism, or entity; and it generallyprecludes derivation from fossil fuels, the latter not being deemed“renewable.”

The terms “biomass precursor species” and “biomass precursor material,”as used (interchangeably) herein, refer to biomass or biomassderivatives from which bio-derived reagents and/or products can besynthesized or otherwise manufactured.

“Fischer-Tropsch products,” as defined herein, refer to molecularspecies derived from a catalytically-driven reaction between CO and H₂(i.e., “syngas”). See, e.g., Dry, “The Fischer-Tropsch process:1950-2000,” vol. 71(3-4), pp. 227-241, 2002; Schulz, “Short history andpresent trends of Fischer-Tropsch synthesis,” Applied Catalysis A, vol.186, pp. 3-12, 1999.

“Isomeric mixtures,” as defined herein, refers to a mixture ofquantities of at least two different molecular species having the samechemical formula and molecular weight, but having a different structuralarrangements—in terms of the atoms making up the at least two differentmolecular species.

3. Diester Lubricant Compositions

In some embodiments, the present invention is generally directed todiester-based lubricant compositions comprising a quantity of at leastone isomeric mixture of diester species having the following chemicalstructures:

wherein R₁, R₂, R₃, and R₄ are the same or independently selected fromC₁ to C₂₀ hydrocarbon groups, and wherein n and m are the same orindependently selected from the group of integers 2 to 20.

In some such above-described compositional embodiments, the kinematicviscosity of the resulting composition at a temperature of 100° C. is atleast 3 mm²/s Additionally or alternatively, in some such compositionalembodiments, said composition has a pour point of less than −20° C.Typically, in such embodiments, diester structures are selected, andadditional components present (if at all), so as to provide for alubricant composition having such aforementioned properties.

In some such above-described compositional embodiments, R₁ and R₂ areindependently selected to have a carbon number from at least about 1 toat most about 15. Additionally or alternatively, in some suchembodiments, R₃ and R₄ are independently selected to have a carbonnumber from at least about 1 to at most about 15. In some or other suchembodiments, n is an integer from 5 to 10. In some or still other suchembodiments, m is an integer from 5 to 10.

In some such above-described compositional embodiments, the isomericdiester species, of which the at least one isomeric mixture iscomprised, each having a molecular mass that is from at least about 400atomic mass units (a.m.u.) to at most about 1100 a.m.u., and moretypically between 450 a.m.u. and 1000 a.m.u.

Referring to the structures in FIG. 1, in some embodiments, the at leastone isomeric mixture of diester species is selected from the group ofisomeric diester pairs consisting of octadecane-1,9-diyl dihexanoate(2a) and octadecane-1,10-diyl dihexanoate (2b); octadecane-1,9-diylbis(decanoate) (3a) and octadecane-1,10-diyl bis(decanoate) (3b);octadecane-1,9-diyl dioctanoate (4a) and octadecane-1,10-diyldioctanoate (4b); ocatadecane-1,9-diyl didodecanoate (5a) andocatadecane-1,10-diyl didodecanoate (5b); and mixtures thereof.

Such above-described compositions are not limited to a single isomericdiester pair. In some such above-described compositional embodiments,such lubricant compositions comprise at least two (i.e., two or more)different isomeric mixtures of diester species. As an example, in someembodiments, a particular lubricant composition may comprise quantitiesof both diester mixture 4a/4b and 5a/5b. In such embodiments, therelative amount of one isomeric mixture of diester species can varyconsiderably from that of another isomeric mixture of diester specieswithin a given lubricant composition.

In some such above-described compositional embodiments, suchcompositions are not limited (at least in terms of theirester-component) to diesters in the form of isomeric mixtures of suchspecies. In some such embodiments, such lubricant compositionsadditionally comprise one or more ester species selected from the groupconsisting of monoesters, diesters, triesters, and combinations thereof.Types of such additional diester species include, but are not limitedto, vicinal diesters such as those described in commonly-assigned U.S.patent application Ser. Nos. 11/673,879 (Miller et al.), filed Feb. 12,2007 and published as United States Patent Publication No. US20080194444 on Aug. 14, 2008; and Ser. No. 12/023,695 (Miller et al.),filed Jan. 31, 2008. Types of such triester species include, but are notlimited to, those described in commonly-assigned U.S. Pat. No.7,544,645, issued on Jun. 9, 2009.

In some such above-described compositional embodiments, such lubricantcompositions comprise, individual diester isomers 1a and 1b, of whichthe isomeric mixture of diester species is comprised, differ in relativeamount by not more than 5 percent. In some or other such embodiments, 1aand 1b differ in relative amount by not more than 3 percent. In some orstill other such embodiments, 1a and 1b differ in relative amount by notmore than 1 percent.

In some particular compositional embodiments, at least one of the atleast one isomeric diester mixtures take the form of 6a and 6b below,wherein R₁, R₂, R₃, and R₄ are selected as described above for 1a and1b.

It is worth noting that in many applications, the above-describeddiesters and their compositions are not used as lubricants bythemselves, but are used as components and/or blending stocks for morecomplex lubricant compositions or mixtures. Accordingly, in some suchembodiments, the above-described compositions further comprise a baseoil selected from the group consisting of Group I oils, Group II oils,Group III oils, and combinations thereof (vide supra). As such, esterswith higher pour points may also be used as blending stocks with otherlubricant oils since they are very soluble in hydrocarbons andhydrocarbon-based oils.

4. Methods of Making Diester Lubricants

As mentioned above, the present invention is additionally directed tomethods of making the above-described (Section 3) lubricant compositionsand/or the diester-based compositions contained therein.

Referring to the flow diagram shown in FIG. 2, in some embodiments,processes/methods for making at least the isomeric diester mixtures ofthe above-mentioned diester-based compositions comprise the followingsteps: (Step 201) converting a quantity of mono-unsaturated free lipidspecies, having a carbon number of from 10 to 22, to an isomeric mixtureof diol species having the same carbon number as the free lipid speciesfrom which they were derived, wherein said converting proceeds via anepoxide intermediate species; and (Step 202) esterifying the isomericmixture of diol species with an esterifying species to form an isomericmixture of diester species, wherein the isomeric mixture of diesterspecies comprises the following isomerically-related structures:

wherein R₁, R₂, R₃, and R₄ are the same or independently selected fromC₂ to C₂₀ hydrocarbon groups, and wherein n and m are the same orindependently selected from the group of integers 2 to 20.

Referring again to FIG. 2, in some such above-described methodembodiments, the step of converting comprises the following sub-steps:(Substep 201 a) epoxidizing the quantity of mono-unsaturated free lipidspecies to yield a quantity of epoxidized lipid species; and (Substep201 b) reducing the epoxidized lipid species to yield an isomericmixture of diol species.

In some such above-described method embodiments, the substep ofepoxidizing (Substep 201 a) utilizes a reagent (i.e., an epoxidizingagent/species) selected from one or more species such as, but notlimited to, peroxides and peroxy acids. Regarding the above-mentionedsubstep of epoxidizing, in some embodiments, the above-describedmono-unsaturated free lipid species (e.g., oleic acid) can be reactedwith a peroxide (e.g., H₂O₂) or a peroxy acid (e.g., peroxyacetic acid)to generate an epoxy-fatty acid species. See, e.g., Swern et al.,“Epoxidation of Oleic Acid, Methyl Oleate and Oleyl Alcohol withPerbenzoic Acid,” J. Am. Chem. Soc., vol. 66(11), pp. 1925-1927, 1944.Another exemplary peroxy acid for use in Substep 201 a ismeta-chloro-peroxybenzoic acid (mCPBA).

In some such above-described method embodiments, the substep of reducingutilizes a metal-hydride reducing agent. Regarding the above-describedsubstep of reducing (Substep 201 b), in some embodiments, lithiumaluminum hydride (LiAlH₄) is used as a reducing agent to effect suchreduction. In some or other embodiments, particularly forindustrial-scale processes, catalytic hydrogenation may be employedusing, for example, copper- or zinc-based catalysts. See, e.g., U.S.Pat. No. 4,880,937; Scrimgeour, “Chemistry of Fatty Acids,” in Bailey'sIndustrial Oil and Fat Products, 6^(th) Edition, Vol. 1, pp. 1-43, F.Shahidi (Ed.), J. Wiley & Sons, New York, 2005.

In some such above-described method embodiments, the step of esterifyingthe isomeric mixture of diol species with an esterifying species firstinvolves conversion of one or more fatty acid species to one or morecorresponding esterification species selected from the group consistingof acyl halide species, it/they selected from the group consisting ofacyl chlorides, acyl bromides, acyl iodides, and combinations thereof;and acyl anhydride species. The esterification species can react withthe —OH groups of the diols to form diester species. In some suchabove-described method embodiments, the step of esterifying the isomericmixture of diol species with an esterifying species involves a catalystselected from the group consisting of an acid catalyst and a basecatalyst.

Regarding the step of esterifying the isomeric mixture of diol speciesto form an isomeric diester mixture, in some embodiments an acid can beused to catalyze the reaction between the —OH groups of the diol and thecarboxylic acid(s). Suitable acids include, but are not limited to,sulfuric acid (Munch-Peterson, Org. Synth., Coll. Vol. 5, p. 762, 1973),sulfonic acid (Allen and Sprangler, Org. Synth., Coll. Vol. 3, p. 203,1955), hydrochloric acid (Eliel et al., Org. Synth., Coll. Vol. 4, p.169, 1963), and phosphoric acid (among others). In some suchembodiments, the carboxylic acid used in this step is first converted toan acyl chloride (or another acyl halide) via, e.g., thionyl chloride orPCl₃. Alternatively, an acyl chloride (or other acyl halide) could beemployed directly. Where an acyl chloride is used, an acid catalyst isnot needed and a base such as pyridine, 4-dimethylaminopyridine (DMAP)or triethylamine (TEA) is typically added to react with an HCl produced.When pyridine or DMAP is used, it is believed that these amines also actas a catalyst by forming a more reactive acylating intermediate.Accordingly, such esterification steps can also be base-catalyzed. See,e.g., Fersht et al., “Acetylpyridinium ion intermediate inpyridine-catalyzed hydrolysis and acyl transfer reactions of aceticanhydride. Observation, kinetics, structure-reactivity correlations, andeffects of concentrated salt solutions,” J. Am. Chem. Soc., vol. 92(18),pp. 5432-5442, 1970; and Hofle et al., “4-Dialkylaminopyradines asHighly Active Acylation Catalysts,” Angew. Chem. Int. Ed. Engl., vol.17, pp. 569-583, 1978. Additionally or alternatively, the carboxylicacid could be converted into an acyl anhydride and/or such species couldbe employed directly.

In some such above-described method embodiments, there further comprisesa step of blending the isomeric mixture of diester species with one ormore other ester species selected from the group consisting oftriesters, diesters, monoesters, and combinations thereof. Such one ormore other ester species, particularly in the case of other diesterspecies, need not be provided as isomeric mixtures. Additionally oralternatively, in some such above-described method embodiments, therefurther comprises a step of blending the isomeric mixture of diesterspecies with a base oil selected from the group consisting of Group Ioils, Group II oils, Group III oils, and combinations thereof.

In some such above-described method embodiments, the isomeric mixture ofdiester species is entirely bio-derived, meaning that the synthesis ofsaid species uses (exclusive of solvents and catalysts) only bio-derivedreagents. In some or other embodiments, such bio-derived isomericmixtures of diester species are subsequently mixed or blended with othercomponents and/or mixtures not entirely of bio-derivation to yieldlubricant compositions that are only partially bio-derived.

Generally, lubricant compositions made by such methods and comprisingsuch diester species have a viscosity of 3 mm²/s (centistokes) or moreat a temperature of 100° C. and they typically have a pour point of lessthan −20° C., and selection of reagents and/or mixture components istypically made with this objective.

In some embodiments, such methods produce compositions (vide supra)comprising at least one isomeric mixture of diester species selectedfrom among the following isomeric diester pairs: octadecane-1,9-diyldihexanoate (2a) and octadecane-1,10-diyl dihexanoate (2b);octadecane-1,9-diyl bis(decanoate) (3a) and octadecane-1,10-diylbis(decanoate) (3b); octadecane-1,9-diyl dioctanoate (4a) andoctadecane-1,10-diyl dioctanoate (4b); ocatadecane-1,9-diyldidodecanoate (5a) and ocatadecane-1,10-diyl didodecanoate (5b); andmixtures thereof. Such isomeric mixtures can be prepared by using oleicacid, or, e.g., methyl oleate, as the initial mono-unsaturated freelipid species.

In some such above-described embodiments, the lubricant compositionsproduced by such methods comprise individual diester isomers 1a and 1bthat differ in relative amount by not more than 5 percent. In some orother such embodiments, 1a and 1b differ in relative amount by not morethan 3 percent. In some or still other such embodiments, 1a and 1bdiffer in relative amount by not more than 1 percent. While notintending to be bound by theory, deviation from equivalent isomeramounts in a given isomeric mixture of diester species can be attributedto one or more scenarios including, but not limited to, rearrangements,solvent effects on transition state, and statistical factors.

In some such above-described method embodiments, the mono-unsaturatedfree lipid species can be a bio-derived fatty acid (or ester) formed byhydrolysis (or esterification) of one or more triglyceride-containingvegetable oils such as, but not limited to, palm oil, sunflower oil,rapeseed oil, olive oil, linseed oil, and the like. Other sources oftriglycerides, for which hydrolysis can yield unsaturated fatty acids,include, but are not limited to, algae, animal tallow, and zooplankton.See, e.g., Bajpai et al., “Biodiesel: Source, Production, Composition,Properties and Its Benefits,” J. Oleo Sci., vol. 55(10), pp. 487-502,2006 (general review); Sargent et al., “Biosynthesis of Lipids inZooplankton from Saanich Inlet, British Columbia, Canada,” MarineBiology, vol. 31, pp. 15-23, 1975 (zooplankton as a source of lipids).

In some embodiments, wherein the above-mentioned hydrolyzed triglyceridesources contain mixtures of saturated fatty acids, mono-unsaturatedfatty acids, and poly-unsaturated fatty acids, one or more techniquesmay be employed to isolate, concentrate, or otherwise separate themono-unsaturated fatty acids from the other fatty acids in the mixture.See, e.g., commonly-assigned United States Patent Application by Millerentitled, “Isolation and Subsequent Utilization of Saturated Fatty Acidsand α-Olefins in the Production of Ester-Based Biolubricants,” Ser. No.12/122,894, filed May 19, 2008.

In some embodiments, partial hydrogenation of polyunsaturated fattyacids can yield mono-unsaturated fatty acids for use in methods of thepresent invention. Post hydrogenation, such mono-unsaturated fatty acidsmay be subjected to one or more of the above-mentionedseparation/isolation techniques. See, e.g., Falk et al., “The Effect ofFatty Acid Composition on Biodiesel Oxidative Stability,” Eur. Journalof Lipid Sci. & Technol., vol. 106(12), pp. 837-843, 2004.

Referring to Scheme 1 (FIG. 3), said scheme being illustrative andrepresentative of some such above-described embodiments, oleic acid (7)is epoxidized with an epoxidizing agent (e.g., a peroxy acid) to yieldepoxy-lipid (epoxy-fatty acid) species 8 (Step 301). With continuedreference to Scheme 1, epoxy-lipid species 8 is reduced, using areducing agent (e.g., LiAlH₄), to an isomeric mixture of diol species(9a/9b) (Step 302). Lastly, the mixture of diol species 9a and 9b isesterified with esterification agent 10 to yield isomeric mixture ofdiester species 6a/6b (Step 303).

Regardless of the source of the mono-unsaturated free lipid species(vide supra), in some embodiments, the carboxylic acids (or their acylderivatives) used in the above-described methods are derived frombiomass. In some such embodiments, this involves the extraction of someoil (e.g., triglyceride) component from the biomass and hydrolysis ofthe triglycerides of which the oil component is comprised so as to formfree carboxylic acids. Other sources of such carboxylic acids include,but are not limited to, those derived (directly or indirectly)

5. Variations

Referring again to FIG. 2, in some embodiments, variations on theabove-described method embodiments are found wherein the step ofconverting comprises the following alternate (variational) sub-steps:(Alt. Substep 201 a′) reducing the quantity of mono-unsaturated freelipid species to yield a quantity of mono-unsaturated fatty alcoholspecies; (Alt. Substep 201 b′) epoxidizing the quantity ofmono-unsaturated fatty alcohol species to yield a quantity of epoxidizedalcohol species; and (Alt. Substep 201 c′) reducing the epoxidizedalcohol species to yield an isomeric mixture of diol species. In somesuch variational embodiments, the variational substeps of reducing thequantity of mono-unsaturated free lipid species and reducing theepoxidized alcohol species utilize one or more metal-hydride reducingagents. In some or other such variational embodiments, the variationalsubstep of epoxidizing the quantity of mono-unsaturated fatty alcoholspecies utilizes an oxidizing agent selected from the group consistingof peroxides and peroxy acids. Generally, all other aspects of suchalternate method embodiments are consistent with the correspondingaspects of the method embodiments described in the preceding section(Section 4).

Referring to Scheme 2 (FIG. 4), said scheme being illustrative andrepresentative of some such above-described alternate methodembodiments, embodiments, oleic acid (7) is reduced with arepresentative reducing agent/species (LiAlH₄) to yield oleoyl alcohol11 (Step 401). Oleoyl alcohol 11 is then epoxidized with an epoxidizingagent (mCPBA) to yield epoxy-alcohol species 12 (Step 402) and theepoxy-alcohol species 12 is reduced with a reducing species to yield anisomeric mixture of diol species 9a and 9b (Step 403). Lastly, theisomeric mixture of diester species 9a and 9b is reacted withesterification agent 10 to yield an isomeric mixture of diester species6a and 6b (Step 404).

Additional and/or alternative variations on the above-described methodsinclude, but are not limited to, generating (and utilizing)compositional ranges of isomeric diester pairs by blending and/or bycompositional variation in the reagents used during the synthesis of thediester species described herein. Compositions produced by such methodvariations will, naturally, be variations themselves. Generally, allsuch variations fall within the scope of the compositions and methodsdescribed herein.

In some additional or alternative variational embodiments, molecularaveraging can be employed to generate greater molecular homogeneity inthe resulting compositions (at least in terms of the diester speciescontained therein) by furthering the homogeneity of the quantity ofmono-unsaturated free lipid species—if not already in a fairlyhomogeneous state. Such molecular averaging techniques involve olefinmetathesis and are generally described in the followingcommonly-assigned United States Patents: U.S. Pat. No. 6,566,568 byChen, issued May 20, 2003; U.S. Pat. No. 6,369,286 by O'Rear, issuedApr. 9, 2002; and U.S. Pat. No. 6,562,230 by O'Rear et al., issued May13, 2003.

In some additional or alternative variational embodiments, at least aportion of the mono-unsaturated free lipid species are initiallysubjected to skeletal isomerization techniques such that the resultinglubricant compositions additionally comprise more highly brancheddiester species. See, e.g., U.S. Pat. No. 6,831,184 (Zhang et al.),issued Dec. 14, 2004, for a method of catalytically-isomerizing fattyacids. Additionally or alternatively, in some such embodiments, suchmore highly branched diester species can be added so as to provide forlubricant compositions comprising additional diester species (videsupra).

6. EXAMPLES

The following examples are provided to demonstrate particularembodiments of the present invention. It should be appreciated by thoseof skill in the art that the methods disclosed in the examples whichfollow merely represent exemplary embodiments of the present invention.However, those of skill in the art should, in light of the presentdisclosure, appreciate that many changes can be made in the specificembodiments described and still obtain a like or similar result withoutdeparting from the spirit and scope of the present invention.

As an exemplary synthetic procedure for making at least an estercomponent of one or more of the diester-based lubricant compositionsdescribed above, the synthesis of isomeric diester mixture 4a and 4b(Scheme 3, FIG. 5) is described in Examples 1-4 which follow. Note thatthis procedure is representative for making isomeric diester mixturesfrom mono-unsaturated free lipid species (e.g., oleic acid), inaccordance with some embodiments of the present invention.

Example 1

This Example serves to illustrate synthesis of mono-unsaturated fattyalcohol 11, in accordance with some embodiments of the presentinvention, and en route to the formation of isomeric diester mixture4a/4b. Referring to Scheme 3 (FIG. 5) oleic acid 7 was reduced to thecorresponding oleoyl alcohol 11 (Step 501) as follows.

To an ice-cold (i.e., in an ice bath) suspension of 43 grams (1.13 mol)of lithium aluminum hydride (LiAlH₄) in tetrahydrofuran (THF) in a3-neck 3-liter reaction flask fitted with an overhead stirrer and areflux condenser, 150 grams (0.53 mol) of oleic acid 7 was addeddrop-wise over a period of 45 minutes via an addition funnel. Theresulting reaction mixture was allowed to warm gradually to roomtemperature, after which the ice bath was replaced with a heating mantleand the reaction mixture was refluxed for 4 hours. After refluxing, thereaction mixture was allowed to cool to room temperature and left tostir overnight. The reaction progress was monitored by infrared (IR) andnuclear magnetic resonance (NMR) spectroscopies for the disappearance ofthe acid carbonyl group. The reaction was worked up by dilution with 500mL of diethyl ether followed by slow addition (drop-wise) of 350 mL of15 wt % NaOH aqueous solution at 0° C. under vigorous stirring, followedby the addition of 50 mL of water. The resulting two-layer solution, awhite solid precipitate and clear organic layer, was filtered to removethe solids (unwanted inorganic salts). The organic layer was dried overanhydrous MgSO₄, filtered, and concentrated on a rotary evaporator(rotovap) to give oleoyl alcohol 11 as colorless oil. The reactionafforded 133 grams (93% yield) of the desired oleoyl alcohol. Theproduct was authenticated with NMR and IR spectroscopic analyses, aswell as gas-chromatographic/mass-spectrometric (GC/MS) analysis.

Example 2

This Example serves to illustrate the synthesis of epoxy-alcohol species12 (oleoyl epoxide), en route to the synthesis of isomeric diestermixture 4a/4b and in accordance with some embodiments of the presentinvention. Referring again to Scheme 3 (FIG. 5), epoxy-alcohol species12 was prepared from oleoyl alcohol 11 (Step 502) according to thefollowing procedure.

To an ice-cold (ice-bath) solution of 52 grams of 75 wt % mCPBA(meta-chloro-peroxybenzoic acid) in 300 mL of methylene chloride(CH₂Cl₂) in a 3-neck 1 L reaction flask, 50 grams of oleoyl alcohol 11,prepared as described above in Example 1, was added drop-wise over a 45minute period. The reaction was allowed to slowly warm to roomtemperature, after which it was left to stir overnight at roomtemperature. The following day, the reaction mixture (solids+clearliquid) was filtered. The filtrate was rinsed once with 150 mL of 10 wt% NaSO₃ aqueous solution, once with 200 mL of saturated KHCO₃ solution,and three times with 300 mL of water. The organic layer was dried overMgSO₄, filtered, and concentrated on a rotary evaporator to give theproduct as a waxy, solid material in 93% yield (48 grams) with highpurity according to GC/MS analysis. Note that methyl oleate was alsoepoxidized using the same epoxidation procedure to give thecorresponding epoxy methyl oleate.

Example 3

With continued reference to Scheme 3 (FIG. 5), this Example serves toillustrate how the epoxy-alcohol species 12 is converted (reduced) to anisomeric mixture of diol species 9a/9b (Step 503), in accordance withsome embodiments of the present invention. Isomeric mixture 9a/9b wasprepared according to the procedure that follows.

To an ice-cold suspension of 20 grams of LiAlH₄ in 350 mL THF in 3-neck2 L reaction flask (fitted with a reflux condenser and an overheadstirrer), 46 grams of epoxy alcohol 12 (synthesized as described abovein Example 2 and dissolved in 200 mL of THF) were added drop-wise over a30 minute period. The resulting mixture was left to warm to roomtemperature and then heated to reflux for few hours. The reaction wasthen allowed to stir at room temperature overnight. The next day, thereaction was placed in an ice-bath and diluted with 300 mL of ether. Theice-cold reaction mixture was treated by slowly adding 200 mL of 15 wt %NaOH solution followed by 30 mL of water with vigorous stirring. Theresulting two phase mixture (liquid layer+white precipitate) wasfiltered and the filtrate dried over MgSO₄, then filtered again andconcentrated to give an isomeric mixture of diol species 9a/9b as awhite powder in 88% yield (41 grams). The diols 9a and 9b wereidentified by spectral analysis (IR, NMR and GCMS). Note that epoxymethyl oleate was similarly reduced with lithium aluminum hydrideaccording to the procedure above to give the diols 9a and 9b describedabove.

Example 4

This Example serves to illustrate the synthesis of isomeric diestermixture 4a/4b, in accordance with some embodiments of the presentinvention. Referring once again to Scheme 3 (FIG. 5), the synthesis ofoctadecane-1,9-diyl dioctanoate/octadecane-1,10-diyl dioctanoate (4a/4b)was carried out via the esterification of diol mixture 9a/9b (Step 504)as follows.

In a 250 mL 3-neck reaction flask fitted with an overhead stirrer,nitrogen bubbler, and Dean-Stark trap, 85.8 grams (0.3 mol) of theisomeric mixture of diol species 9a/9b (prepared as described above inExample 3) was mixed with 129.6 grams (0.9 mol) of octanoic acid and2.76 grams of 85 wt % H₃PO₄ at room temperature. The resultant mixturewas stirred and heated to 160° C. with nitrogen bubbling through themixture. After 8 hours, the reaction was complete and was cooled to roomtemperature. The mixture was stirred with sodium bicarbonate (3 grams)for 30 minutes and then filtered. The mixture was distilled under avacuum of 10 mm Hg (Torr) to remove excess octanoic acid. The desireddiester product 4a/4b was obtained in 75% yield. The lubrication andphysical properties of diester product 4a/4b are shown in Table 1 (FIG.6).

7. Summary

In summary, the present invention provides for diester-based lubricantcompositions comprising isomeric mixtures of diester species. Thepresent invention also provides for methods (processes) of making theseand other similar lubricant compositions. In some embodiments, themethods for making such diester-based lubricants utilize abiomass-derived precursor comprising mono-unsaturated fatty acids and/oresters, wherein such mono-unsaturated fatty acids/esters are convertedto one or more isomeric diol species en route to the synthesis ofdiester-based lubricant compositions. Subsequent steps on the path tosuch synthesis may employ carboxylic acids and/or acylhalides/anhydrides derived from biomass and/or Fischer-Tropschsynthesis. In some such embodiments, at least the isomeric mixtures ofdiester species, of which the diester-based lubricant compositions arecomprised, are entirely bio-derived.

All patents and publications referenced herein are hereby incorporatedby reference to the extent not inconsistent herewith. It will beunderstood that certain of the above-described structures, functions,and operations of the above-described embodiments are not necessary topractice the present invention and are included in the descriptionsimply for completeness of an exemplary embodiment or embodiments. Inaddition, it will be understood that specific structures, functions, andoperations set forth in the above-described referenced patents andpublications can be practiced in conjunction with the present invention,but they are not essential to its practice. It is therefore to beunderstood that the invention may be practiced otherwise than asspecifically described without actually departing from the spirit andscope of the present invention as defined by the appended claims.

What is claimed is:
 1. A lubricant composition comprising at least oneisomeric mixture of diester species comprising the followingisomerically-related diester structures:

wherein R₁, R₂, R₃, and R4 are the same or independently selected fromC₁ to C₂₀ hydrocarbon groups, and wherein n is independently selectedfrom the group of integers 2 to 20, and m=2, the structure representedby (1a) being a vicinal ester.
 2. The lubricant composition of claim 1wherein the kinematic viscosity of the lubricant composition attemperature of 100° C. is at least 3 mm²/s.
 3. The lubricant compositionof Claim1, said composition having a pour point of less than −20° C. 4.The lubricant composition of claim 1, wherein R₁ is selected to have acarbon number from at least about 1 to at most about
 15. 5. Thelubricant composition of claim 1, wherein R₂ is selected to have acarbon number from at least about 1 to at most about
 15. 6. Thelubricant composition of claim 1, comprising at least two differentisomeric mixtures of diester species.
 7. The lubricant composition ofclaim 1, wherein n is selected from the group of integers 5 to
 10. 8.The lubricant composition of claim 1, wherein said composition comprisesquantities of at least two different isomeric mixtures of diesterspecies.
 9. The lubricant composition of claim 1, wherein the isomericdiester species, of which the at least one isomeric mixture iscomprised, have a molecular mass that is from at least about 400 a.m.u.to at most about 1100 a.m.u.
 10. The lubricant composition of claim 1,further comprising a base oil selected from the group consisting ofGroup I oils, Group II oils, Group III oils, and combinations thereof.11. The lubricant composition of claim 1, further comprising one or moreester species selected from the group consisting of monoesters,diesters, triesters, and combinations thereof.
 12. The lubricantcomposition of claim 1, wherein individual diester isomers 1a and 1b, ofwhich the isomeric mixture of diester species is comprised, differ inrelative amount by not more than 5 percent.